This document outlines guidance for measuring radon-222 activity concentration and the potential alpha energy concentration of its short-lived decay products in the air. The measurement methods fall into three categories: a) spot measurement methods; b) continuous measurement methods; c) integrated measurement methods. This document provides several methods commonly used for measuring radon-222 and its short-lived decay products in air. This document also provides guidance on the determination of the inherent uncertainty linked to the measurement methods described in its different parts.